N
 Node parameter type@Beta public interface Graph<N>
A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
There are three main interfaces provided to represent graphs. In order of increasing
complexity they are: Graph
, ValueGraph
, and Network
. You should generally
prefer the simplest interface that satisfies your use case. See the
"Choosing the right graph type" section of the Guava User Guide for more details.
Graph
supports the following use cases (definitions of
terms):
Graph
explicitly does not support parallel edges, and forbids implementations or
extensions with parallel edges. If you need parallel edges, use Network
.
Graph
The implementation classes that `common.graph` provides are not public, by design. To create
an instance of one of the builtin implementations of Graph
, use the GraphBuilder
class:
MutableGraph<Integer> graph = GraphBuilder.undirected().build();
GraphBuilder.build()
returns an instance of MutableGraph
, which is a subtype
of Graph
that provides methods for adding and removing nodes and edges. If you do not
need to mutate a graph (e.g. if you write a method than runs a readonly algorithm on the graph),
you should use the nonmutating Graph
interface, or an ImmutableGraph
.
You can create an immutable copy of an existing Graph
using ImmutableGraph.copyOf(Graph)
:
ImmutableGraph<Integer> immutableGraph = ImmutableGraph.copyOf(graph);
Instances of ImmutableGraph
do not implement MutableGraph
(obviously!) and are
contractually guaranteed to be unmodifiable and threadsafe.
The Guava User Guide has more information on (and examples of) building graphs.
See the Guava User Guide for the common.graph
package ("Graphs Explained") for
additional documentation, including:
Modifier and Type  Method and Description 

Set<N> 
adjacentNodes(Object node)
Returns the nodes which have an incident edge in common with
node in this graph. 
boolean 
allowsSelfLoops()
Returns true if this graph allows selfloops (edges that connect a node to itself).

int 
degree(Object node)
Returns the count of
node 's incident edges, counting selfloops twice (equivalently,
the number of times an edge touches node ). 
Set<EndpointPair<N>> 
edges()
Returns all edges in this graph.

boolean 
equals(Object object)
Returns
true iff object is a Graph that has the same elements and the
same structural relationships as those in this graph. 
boolean 
hasEdge(Object nodeU,
Object nodeV)
Returns true if there is an edge directly connecting
nodeU to nodeV . 
int 
hashCode()
Returns the hash code for this graph.

int 
inDegree(Object node)
Returns the count of
node 's incoming edges (equal to predecessors(node).size() )
in a directed graph. 
boolean 
isDirected()
Returns true if the edges in this graph are directed.

ElementOrder<N> 
nodeOrder()
Returns the order of iteration for the elements of
nodes() . 
Set<N> 
nodes()
Returns all nodes in this graph, in the order specified by
nodeOrder() . 
int 
outDegree(Object node)
Returns the count of
node 's outgoing edges (equal to successors(node).size() )
in a directed graph. 
Set<N> 
predecessors(Object node)
Returns all nodes in this graph adjacent to
node which can be reached by traversing
node 's incoming edges against the direction (if any) of the edge. 
Set<N> 
successors(Object node)
Returns all nodes in this graph adjacent to
node which can be reached by traversing
node 's outgoing edges in the direction (if any) of the edge. 
Set<N> nodes()
nodeOrder()
.Set<EndpointPair<N>> edges()
boolean isDirected()
source node
to a target node
, while
undirected edges connect a pair of nodes to each other.boolean allowsSelfLoops()
IllegalArgumentException
.ElementOrder<N> nodeOrder()
nodes()
.Set<N> adjacentNodes(Object node)
node
in this graph.Set<N> predecessors(Object node)
node
which can be reached by traversing
node
's incoming edges against the direction (if any) of the edge.
In an undirected graph, this is equivalent to adjacentNodes(Object)
.
Set<N> successors(Object node)
node
which can be reached by traversing
node
's outgoing edges in the direction (if any) of the edge.
In an undirected graph, this is equivalent to adjacentNodes(Object)
.
This is not the same as "all nodes reachable from node
by following outgoing
edges". For that functionality, see Graphs.reachableNodes(Graph, Object)
.
int degree(Object node)
node
's incident edges, counting selfloops twice (equivalently,
the number of times an edge touches node
).
For directed graphs, this is equal to inDegree(node) + outDegree(node)
.
For undirected graphs, this is equal to adjacentNodes(node).size()
+ (1 if node
has an incident selfloop, 0 otherwise).
If the count is greater than Integer.MAX_VALUE
, returns Integer.MAX_VALUE
.
int inDegree(Object node)
node
's incoming edges (equal to predecessors(node).size()
)
in a directed graph. In an undirected graph, returns the degree(Object)
.
If the count is greater than Integer.MAX_VALUE
, returns Integer.MAX_VALUE
.
int outDegree(Object node)
node
's outgoing edges (equal to successors(node).size()
)
in a directed graph. In an undirected graph, returns the degree(Object)
.
If the count is greater than Integer.MAX_VALUE
, returns Integer.MAX_VALUE
.
boolean hasEdge(Object nodeU, Object nodeV)
nodeU
to nodeV
. This is
equivalent to return nodes().contains(nodeU) && successors(nodeU).contains(nodeV)
.
In an undirected graph, this is equal to hasEdge(nodeV, nodeU)
.
boolean equals(@Nullable Object object)
true
iff object
is a Graph
that has the same elements and the
same structural relationships as those in this graph.
Thus, two graphs A and B are equal if all of the following are true:
directedness
.
node sets
.
edge sets
.
Graph properties besides directedness
do not affect equality.
For example, two graphs may be considered equal even if one allows selfloops and the other
doesn't. Additionally, the order in which nodes or edges are added to the graph, and the order
in which they are iterated over, are irrelevant.
A reference implementation of this is provided by AbstractGraph.equals(Object)
.
int hashCode()
edges()
.
A reference implementation of this is provided by AbstractGraph.hashCode()
.
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